Exemplary of the prior art in the general animal trap area is U.S. Pat. No. 3,060,623, J. R. Aldrich, issued Oct. 30, 1962, and entitled "Animal Trap".
The Aldrich device includes two arms with a coil spring between the arms tending to bias them apart, with means at the non-spring end of one of the arms for supporting a trip lever, the lever having inter-engagement portions which retain the other of the spring arms downwardly against the first arm until the trip lever has been depressed, at which point the arms are disengaged from each other, and the one arm flies upwardly with respect to the other. A noose-like cable is positioned to surround the general location of the trip lever, and the cable is then entrained over a catch portion at the non-spring end of the upwardly snapping arm, the other end of the cable being anchored in some way, as to a tree. When the animal presses downwardly on the trip lever, the two arms are disengaged from each other, and spring apart. In so doing, the cable is suddenly jerked tight, and the noose tightens around the foot of the animal.
While the basic construction of Aldrich is simple and reliable in terms of entrapping the animal without causing undue injury, it does not include an provision for protecting the animal against injury after it has become ensnared. Any violet attempt by the animal to free itself by lunging away from the trap could cause physical damage due to the forces exerted on the snared part of the animal. Also, the Aldrich trap is not designed to allow the escape of animals larger than those intended to be caught.